


Tipping point

by ShadeDuelist



Series: Shade in Undertail: The Undertale Sinful Timelines Collection [5]
Category: Undertale (Video Game)
Genre: Alternate universe - Wastelandfell, M/M
Language: English
Status: Completed
Published: 2016-05-30
Updated: 2016-05-30
Packaged: 2018-06-10 02:10:01
Rating: Explicit
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 1,770
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6933793
Author URL: https://archiveofourown.org/users/ShadeDuelist/pseuds/ShadeDuelist
Summary: <blockquote class="userstuff">
              <p>(Based on the Wastelandfell AU thought up by Queennati!)</p><p>Prolonged exposure to Mettaton, his brother's lover, isn't doing Sans any favors.  Slowly but surely, he grows needier and needier, until he has to do something about it.</p><p>Then again, so does Mettaton...</p>
            </blockquote>





	Tipping point

“o-oh god…” Sans was in _bad_ shape. After such a long time of seeing Mettaton prance around in his and Papyrus’ humble abode, being all flirty and touchy-feely with both his brother and himself, posing dramatically on workbenches and swaying those firm metal hips of his every chance he got… after such a long, _long_ time of feeling the pleasurebot’s dainty hands on his arm, his hand, sometimes even his sternum or his hips for mere fractions of a second beyond what would be appropriate before almost innocently moving away again… Mettaton was such a damn _tease_ , and it was driving him up the walls with how well it was working. He wasn’t supposed to be into the bot, as Mettaton was _absorbed_ by Papyrus and his constant attention and didn’t even seem to notice him at all, not in _that way_ at least, but… _damn it_ , he was just a monster too! He had needs too! He’d had too many nights where Papyrus and Mettaton’s moans kept him out of his sleep, and that did nothing but make things worse, causing him to yearn for the pleasurebot to moan for _him_ as well… But the true breaking point, the true moment where the scales had been tipped, had happened only five minutes before, when he’d walked in on Mettaton changing out of Papyrus’ old coveralls, showing off his perfect ass obliviously, and the sight had had Sans’ magic instantly materialize, tangible and painfully sensitive, on his pelvic bone. It was all he could do to close the door again as soundlessly as possible and walk away to the back of the warehouse he and his brother used as their home. There, behind some crates next to the door, protected from the occasional exposure to sand and the elements by a tarp, he sank to the floor, unfastening his pants and opening them just enough for his magical length to spring free. Bony hand closing around his slightly glowing dick, he felt far too frustrated for subtlety and decided to instantly go for broke: the first pump he gave to his member saw its faint glow intensify and had him lean back. “oh fuckin’ _god…_ that’s it, yeah…” Thinking back on Mettaton as he’d stood there, leaning slightly forward, those perfectly rounded asscheeks looking so soft and supple and so _reachable_ , Sans gritted his teeth and gasped softly, biting back a louder moan as his bony thumb flicked over the sensitive head of his magic dick. “ _holy shit…_ y-ya shouldn’t be so god-damned _good_ at it, metta… ya oughta _suck_ at bein’ a damn whore…” Sans’ eyes closed despite his tension, and his hand grasped his magic-turned-physical a little more tightly as he picked up more speed. “ahh, _fuck it_ … paps needs you bad, metta, but not as bad as i do… _nowhere near as fuckin’ bad as i need ya_ , metta… d-damn it… h-how could i ever… how could i… _ahh y-yeah…_ ” What little modesty Sans still retained, it flew out of the window as he started thrusting his hips subtly but very deliberately into his strokes, fucking his hand just as he would fuck the pleasurebot if he ever got the chance - which would be _never_ , he told himself again, biting back a sob that surprised him. “g-god, ‘m so pathetic…!”, he whined to himself, running his thumb over the head of his glowing dick again and smearing the tiniest droplet of precum over the porous surface of his phalanx-

“Oh, I wouldn’t call you ‘pathetic’, Sans, _darling…_ ” Out of nowhere, Mettaton’s voice drifted over to him, and Sans started, sitting up again, eyes wide. Oh shit. Sure enough, there was the pleasurebot, leaning against the wall, looking him over with mild amusement in his gaze. Oh _hell_. “...In fact, ‘pathetic’ is the _last_ word I’d think of using, Sansy~”, the robot crooned lowly, walking over to him, and Sans made to react with extra venom to cover up the fact that he’d been communing with himself, only to find the words fail him the next second.

Mettaton was _completely naked._

_Oh hell._

“...f-fuck.” It was said flatly, without any kind of bite or emotion; Sans had no idea what he was supposed to think of the situation. Mettaton stood right next to him now, not a single shred of clothing on his metal body, his own robotic dick standing at attention and glowing a dark pink, and he looked at him like he was a delicacy served up for his personal enjoyment. Then, after a few seconds of tense silence, Mettaton laughed, lightly and unnervingly, before grinning.

“Well, Sans, if you _insist…_ ” Before Sans had any chance to react, the former pleasurebot stood over him, and a split second later saw him lowering himself down onto his knees, moving back a little and settling his ass flush against Sans’ length, his silicon asscheeks pressing warmly and comfortably against the shaped magic that was still glowing bright red. “Mmm, you feel nice…”

“f-fuckin’ hell…”, Sans stammered, looking at Mettaton, torn between pushing him away and grasping hold of him. He wanted so badly to do the latter, but his love for his brother had him feel compelled to do the former. “p-paps-”

“Papyrus is a big boy, he can handle himself without me for a little while - and don’t you think your brother wants you to be happy, too, Sans? Don’t you think your brother wants to see you fulfilled?” As Mettaton spoke, he began slowly rocking himself back against Sans’ dick, his plush asscheeks rubbing against the magic it was formed out of with surprising softness, drawing pleasure of a very different kind from Sans. A shaky sigh escaped the skeleton, but he didn’t stop resisting just yet, and Mettaton let out a soft ‘tsk’ before speaking in his low, seductive voice again: “Oh, Sans… _don’t you think you deserve this?_ ” Another, more firm backwards motion had Sans’ magic, sensitive as it was, forced to accommodate the metallic body that was pressed against it and forced a gasp from Sans.

“g-god damn…!”

“Come on, Sans… be honest to yourself for once… I love Papyrus, yeah, but _sex_ isn’t _love_ and you are always so good to me, you _deserve_ a little treat…”, Mettaton said, leaning a little lower before whispering to Sans. “ _This is all me, Sans… I need it too… I need you, too…_ ” Sans’ resistance crumbled in a single flutter of hs soul: he grasped Mettaton’s leg firmly and looked at him with a desperate expression.

“metta… c-c’mon then…”

“Mmm, alright then…” Mettaton rocked back again, and Sans felt liquid bead on his head and form droplets that rolled down it, even though the warehouse was always a few degrees cooler than the outside. His bones shivered and rattled quietly as Mettaton’s hips canted backwards and his perfect, round ass pressed so tightly against his magic erection… “Oh, Sans, baby… you’re holding back on me, darling. Let it go… let it _all_ go…” Mettaton’s slender hand carefully caressed up his sternum and then, over his clavicle to his neck and from there to his jaw, tilting his head up so Sans had no choice but to look into Mettaton’s four red eyes which regarded him with pride. Was he feeling _proud_ of making Sans feel like he was falling apart?

Sans couldn’t help but feel infuriated by that deep down. Mettaton had been a pleasurebot, but that had already been a while ago now, after Papyrus had been so daring - or stupid, depending on what mood he was in when he pondered the matter - to ‘rescue’ the robot he’d fallen for. Mettaton had adapted to life in the wilderness surprisingly well, but occasionally, he showed a little part of himself that _hadn’t_ adapted yet, and Sans was angry each and every time that happened, because he felt like it meant that they weren’t getting through to the former pleasurebot. This was no different - but his frustration gave a different impetus to his anger. Instead of launching into an angry rant about his past and growing past it, like he usually did, Sans mentally decided that Mettaton acting like a pleasurebot justified him _treating_ the robot as such.

“nnngh…!” He grabbed Mettaton’s ass and thrust against him, only for Mettaton’s eyes to widen and a moan to be ripped from him.

“ _Ahh…!_ S-sans… careful now… save some for later… d-don’t be greedy…” Mettaton gently grasped Sans’ right hand and entwined their fingers, looking down warmly at the skeleton underneath him. “...There’s plenty of time, Sans… I want you to _last_ … y-you look so amazing, so hot… A-and you’re so _big_ , Sansy, s-so… so _ready_ for this…” The grin on Mettaton’s features could be described undelicately as ‘shit-eating’ and ‘smug’, but Sans went with ‘promising’ considering the robot’s previous words.

“f-f- _fuuuuck…_ ”, he groaned. Mettaton’s fingers entwined with his, the way the robot was still rocking back his perfect ass against his magic dick, which was now glowing even brighter with all the pent up need threatening to spill over and sweep him off… it was too much, too intense, and Sans found himself gritting his teeth. “y-ya wanna _wreck_ me o-or what, metta?”

“Oh, no… no, no, Sans, darling…” Mettaton’s grip tightened as the robot leaned down again to lick along Sans’ jaw before whispering the remainder of his answer. “ _I want to fuck you, Sans…_ “

“h-holy fuck… y-yeah…!”, Sans said, and just like that, Mettaton lifted himself off Sans, settling back a second later, only this time slowly sinking Sans’ tangible magic inside of himself, groaning in perfect tandem with the skeleton. His hand, still entwined with Sans’, clenched tightly as his body stretched to accommodate the invasion, but Sans was beyond caring about that, instead gripping Mettaton’s hand back just as tightly to ground himself, threatening to go off from the almost unbearably tight hold the pleasurebot’s tight insides had on his magic dick. “g-god fuckin’... h-how’s paps even _last_ …?”

“Y-your brother has good self control… h-he’s surprisingly… pent up…”, Mettaton huffed out, gripping Sans’ jaw a little more demandingly before speaking in a heated tone: “N-now you’d better not… _ahh_ … h-hold out on m-me…”

“...stars a-al-f-fuckin’-mighty…”, Sans groaned superfluously, feeling his entire body glow with magic at that point, his magic feeling sensitive to the point of bordering on painful as Mettaton’s metallic body squeezed it. “p-promise… if ya f-fuck me well… you’re gettin’ _all of it_ , metta…”, he ground out, eyes glowing, allowing the pleasure of Mettaton riding him to blank out all other thoughts the next second.

All but one.

‘ _Finally…’_

 


End file.
